In ruminants, ingested feed first passes into the rumen, where it is pre-digested or degraded by fermentation. During this period of fermentation the ingested feed may be regurgitated to the mouth where it is salivated and masticated. After a period of fermentation regulated by natural processes and variable depending on the animal and the feedstuff, absorption of digested nutrients starts and continues in the subsequent sections of the digestive tract by the ruminant animal. This process is described in detail by D. C. Church, "Digestive Physiology and Nutrition of Ruminants", Vol. 1, O.S.U. Book Stores, Inc., of Corvallis, Oreg.
The rumen, the largest of the four stomach compartments of ruminants, serves as an important location for metabolic breakdown of ingested foodstuffs through the action of microorganisms which are present therein. Ingested food is typically retained in the rumen for from about 6 to 30 hours during which time it is subject to metabolic breakdown by the rumen microorganisms. Much ingested protein material is broken down in the rumen to soluble peptides and amino acids and utilized by the rumen microorganisms. When the rumen contents pass into the abomasum and intestine, the microbial mass is digested, thus providing protein to the ruminant. Thus, the natural nutritional balance of the ruminant animal is primarily a function of the microbial composition and population.
In preparing nutrients and medicaments intended for administration to ruminants, it is important to protect the active ingredients against the environmental conditions of the rumen, i.e., microbial degradation and the effects of a pH of about 5.5, so the active substance will be saved until it reaches the particular location where absorption takes place. It is well known that the rate of meat, wool and/or milk production can be increased if sources of growth limiting essential amino acids, and/or medicaments, are protected from alteration by microoganisms residing in the rumen and become available for direct absorption by the animal later in the gastrointestinal tract.
Materials which protect the core against degradation by the rumen contents should be resistant to attack by the rumen fluid which contains enzymes or microorganisms but must make the active ingredient available rapidly in the more acidic fluid of the abomasum at a pH within the normal physiological range of about 2 to about 3.5. To more easily coat or encapsulate active ingredients in protective materials, the protective materials should be soluble in certain organic solvents for coating purposes.
Because proteins are subject to breakdown in the rumen, it has been suggested that protein-containing nutrients fed to ruminants be treated so as to permit passage without microbial breakdown through the rumen to the abomasum. Suggested procedures have included coating the protein material, for example, with fats and vegetable oils; heat treating of the protein material; reacting the protein material with various compounds such as formaldehyde, acetylenic esters, polymerized unsaturated carboxylic acid or anhydrides and phosphonitrilic halides, etc.
It is well known that all proteins found in animal and plant life are chemical compounds containing different combinations of over 20 amino acids, the number and arrangement of such acids being fixed in any particular protein. Twelve of these amino acids can be synthesized in nutritonally adequate amounts from other substances by biochemical processes normally present in most animals, but the remaining 10 essential amino acids are not synthesized in sufficient quantities and must be ingested by the animal. Since the proportions of the constituent amino acids in a particular protein cannot be varied, the essential amino acid least in supply limits the amounts of that protein which can be produced by the animal. Consequently, for any given diet, there will be a particular essential amino acid which limits the production of protein incorporating that essential amino acid unless, of course, two or more such amino acids are equally limiting.
The application of the above principles leads to the formulation of diets for nonruminant animals which provide the optimum proportion of amino acids and have enabled significant increases in protein production to be achieved. In the ruminant, dietary proteins and amino acids are, to a variable extent, broken down to ammonia and various organic compounds by microbial fermentation in the first two compartments of the stomach (the rumen and reticulum). The bacteria and protozoa in these organs utilize these metabolites for their own growth and multiplication and the microbial protein so formed passes on to the abomasum, the compartment of the stomach corresponding to the stomach of nonruminants, where it is partially digested. The process is completed in the small intestine and the amino acids are absorbed.
It is likewise well-known that medicaments are more effective when they are protected from the environment of the rumen. See, for example, U.S. Pat. Nos. 3,041,243 and 3,697,640.
Of interest is U.S. Pat. No. 4,177,255 which discloses a polymeric matrix having a substance dispersed therein which is stable in the rumen but leachable from the matrix postruminally. This patent discloses that the matrix is continuous. From this, it is concluded that there is no alignment of the dispersed substance forming a continuous path entirely through the coating.
Also of interest is published European Application No. 77,264 which discloses a coating obtained by combining a copolymer sensitive to variations in pH with a polymer insensitive to variations in pH and optionally an organic acid, the second polymer improving the liberation of the active substance at a pH between 1 and 2.5 and decreasing is extractability in aqueous media.
Other U.S. patents of interest which disclose rumen stable coating compositions comprising a polymer having basic amino groups and one or more substances dispersed therein include U.S. Pat. Nos. 4,181,708, 4,181,709 and 4,181,710. The present invention provides a coating for protecting a core of a material beneficial to ruminants (e.g., nutrients, medicament, etc.). The coating consists of a pH insensitive portion and a pH sensitive portion, allowing the core to be exposed in a predetermined environment.
Sometimes, pH sensitive coating materials are more expensive than pH insensitive, and the present invention therefore provides a more economical coating. Also, pH sensitive coatings are sometimes more subject to mechanical damage during processing of animal feed materials which obviously destroys their utility. The present invention therefore provides for a more versatile coating which may result in a more economical coating which is more resistant to mechanical damage from processing equipment.